7 Units of Measurements
The
metre is the length of the path travelled by light in vacuum during a
time interval of 1/299 792 458 of a second.
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kilogram (kg)
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second
(s)
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The
second is the duration of 9 192 631 770 periods of the radiation
corresponding to the transition between the two hyperfine levels of the
ground state of the caesium 133 atom.
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ampere
(A)
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The
ampere is the intensity of a constant current which, if maintained in two
straight parallel conductors of infinite length, of negligible circular
cross-section, and placed 1 metre apart in vacuum, would produce
between these conductors a force equal to 2 x 10-7 newton per metre of
length.
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kelvin
(K)
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The
kelvin is the fraction 1/273,16 of the thermodynamic temperature of the
triple point of water.
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candela
(cd)
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The
candela is the luminous intensity, in a given direction, of a source
that emits monochromatic radiation of frequency 540 x 1012 hertz and
that has a radiant intensity in that direction of 1/683 watt per
steradian
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mole
(mol)
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The
mole is the amount of substance of a system which contains as many
elementary entities as there are atoms in 0,012 kilogram of carbon 12.
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